The invention relates to an apparatus for the automatic mechanical centering and clamping of elongate round bodies of various diameter of wood, metal or plastic, on which processing operations are to be carried out which are oriented to the central longitudinal axes of the round bodies clamped in place. This may concern sizing of the trunk circumference of round timber, or faceworking of the ends or chamfering of the same, for example on pipe ends to prepare for welds.
A specific example of such processing is the circular milling of the root ends of tree trunks, to obtain sized round timbers for their trouble-free further processing. Such an apparatus for the milling off of root swellings on tree trunks is described in German Offenlegungsschrift No. 33 06 569, in which the tree trunk, clamped in place, has a milling tool circling around its root end. The tree trunk is supported on two support bearings arranged axially one behind the other and is clamped against rotation during a milling-off by a hold-down device acting from above. In order to ensure that the central longitudinal axes of tree trunks which vary in their diameters are always aligned with the circling axis of the milling tool, the two support bearings have a V-shaped bearing profile symmetrical to the vertical centering plane, and the bearings are also vertically adjustable. While alignment of the tree trunks in the vertical centering plane, in other words in horizontal direction, by the V-shaped bearing profile of the two support bearings is performed more or less automatically, for alignment in the horizontal centering plane the two support bearings have to be adjusted vertically. This may be carried out visually by simple eye judgement or, with a correspondingly more complex apparatus, by optoelectrical measuring equipment. Only when a tree trunk has its longitudinal axis aligned to and centered with the circulating axis of the milling tool can it be clamped against rotation by the hold-down device acting from above. This known centering and clamping arrangement for tree trunks therefore requires relatively expensive apparatus and is time consuming. In addition, it often does not satisfy the required accuracy.
In the case of centering apparatuses for veneer peeling machines, it is already known from German Patent No. 11 72 028 to center round timbers automatically and mechanically, without special measuring facilities. This is effected in principle in the case of the centering apparatus described there by three centering levers each of which is pivoted by a common drive, in the manner of an iris diaphragm, synchronously inward into the mouth-shaped opening of two jaw arrangements arranged at an axial distance from each other. Apart from the fact that no clamping against rotation of the round timbers is required in the case of this known centering apparatus specifically intended for veneer peeling machines, a considerable disadvantage of this known centering device is to be seen above all in the fact that the construction expenditure for the synchronous pivoting of the three centering levers is very great. For instance, apart from the three centering levers with their three pivot axes, two further control levers with additional four joints are required, which not only involves great manufacturing expense but is also susceptible to operational faults.